Delphi Programming Guide
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Part I - Foundations
  Chapter 1 – Delphi 7 and Its IDE
  Chapter 2 – The Delphi Programming Language
  Chapter 3 – The Run-Time Library
  Chapter 4 – Core Library classes
  Chapter 5 – Visual Controls
  Chapter 6 – Building the User Interface
  Chapter 7 – Working with Forms
Part II - Delphi Object-Oriented Architectures
  Chapter 8 – The Architecture of Delphi Applications
  Chapter 9 – Writing Delphi Components
  Chapter 10 – Libraries and Packages
  Chapter 11 – Modeling and OOP Programming (with ModelMaker)
  Chapter 12 – From COM to COM+
Part III - Delphi Database-Oriented Architectures
  Chapter 13 – Delphi's Database Architecture
  Chapter 14 – Client/Server with dbExpress
  Chapter 15 – Working with ADO
  Chapter 16 – Multitier DataSnap Applications
  Chapter 17 – Writing Database Components
  Chapter 18 – Reporting with Rave
Part IV - Delphi, the Internet, and a .NET Preview
  Chapter 19 – Internet Programming: Sockets and Indy
  Chapter 20 – Web Programming with WebBroker and WebSnap
  Chapter 21 – Web Programming with IntraWeb
  Chapter 22 – Using XML Technologies
  Chapter 23 – Web Services and SOAP
  Chapter 24 – The Microsoft .NET Architecture from the Delphi Perspective
  Chapter 25 – Delphi for .NET Preview: The Language and the RTL
  Appendix A – Extra Delphi Tools by the Author
  Appendix B – Extra Delphi Tools from Other Sources
  Appendix C – Free Companion Books on Delphi
  List of Figures    
  List of tables    
  List of Listings    
  List of Sidebars  

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Working with HTTP

Handling mail messages is certainly interesting, and mail protocols are probably still the most widespread Internet protocols. The other popular protocol is HTTP, which is used by web servers and web browsers. I'll devote the rest of this chapter to this protocol (along with a discussion of HTML); the following two chapters also discuss it.

On the client side of the Web, the main activity is browsing—reading HTML files. Besides building a custom browser, you can embed the Internet Explorer ActiveX control within your program (as I've done in the WebDemo example in Chapter 12, "From COM to COM+"). You can also directly activate the browser installed on the user's computer—for example, opening an HTML page by calling the ShellExecute method (defined in the ShellApi unit):

ShellExecute (Handle, 'open', FileName, '', '', sw_ShowNormal);

Using ShellExecute, you can simply execute a document, such as a file. Windows will start the program associated with the HTM extension, using the action passed as the parameter (in this case, open, but passing nil would have invoked the standard action producing the same effect). You can use a similar call to view a website, by using a string like "" instead of a filename. In this case, the system recognizes the http section of the request as requiring a web browser and launches it.

On the server side, you generate and make available the HTML pages. At times, it may be enough to have a way to produce static pages, occasionally extracting new data from a database table to update the HTML files as needed. In other cases, you'll need to generate pages dynamically based on a request from a user.

As a starting point, I'll discuss HTTP by building a simple but complete client and server; then I'll move on to discuss HTML producer components. In Chapter 20, I'll move from this "core technology" level to the RAD development style for the web supported by Delphi, introducing the web server extension technologies (CGI, ISAPI, and Apache modules) and discussing the WebBroker and WebSnap architectures.

Grabbing HTTP Content

As an example of the use of the HTTP protocols, I've written a specific search application. The program hooks onto the Google website, searches for a keyword, and retrieves the first 100 sites found. Instead of showing the resulting HTML file, the program parses it to extract only the URLs of the related sites to a list box. The description of these sites is kept in a separate string list and is displayed as you click a list-box item. So, the program demonstrates two techniques at once: retrieving a web page and parsing its HTML code.

To demonstrate how you should work with blocking connections, such as those used by Indy, I've implemented the program using a background thread for the processing. This approach also gives you the advantage of being able to start multiple searches at once. The thread class used by the WebFind application receives as input a URL to look for, strUrl.

The class has two output procedures, AddToList and ShowStatus, to be called inside the Synchronize method. The code of these two methods sends some results or some feedback to the main form, respectively adding a line to the list box and changing the status bar's SimpleText property. The key method of the thread is Execute. Before we look at it, however, here is how the thread is activated by the main form:

  strSearch = '';
procedure TForm1.BtnFindClick(Sender: TObject);
  FindThread: TFindWebThread;
  // create suspended, set initial values, and start
  FindThread := TFindWebThread.Create (True);
  FindThread.FreeOnTerminate := True;
  // grab the first 100 entries
  FindThread.strUrl := strSearch + EditSearch.Text +'&num=100';

The URL string is made of the main address of the search engine, followed by some parameters. The first, as_q, indicates the words you are looking for. The second, num=100, indicates the number of sites to retrieve; you cannot use numbers at will but are limited to a few alternatives, with 100 being the largest possible value.


The WebFind program works with the server on the Google website at the time this book was written and tested. The custom software on the site can change, however, which might prevent WebFind from operating correctly. This program was also in Mastering Delphi 6; however, it was missing the user agent HTTP header, and after a while Google changed its server software and blocked the requests. Adding any value for the user agent fixed the problem.

The thread's Execute method, activated by the Resume call, calls the two methods doing the work (shown in Listing 19.1). In the first, GrabHtml, the program connects to the HTTP server using a dynamically created IdHttp component and reads the HTML with the result of the search. The second method, HtmlToList, extracts the URLs referring to other websites from the result, the strRead string.

Listing 19.1: The TFindWebThread Class (of the WebFind Program)
Start example
unit FindTh;
  Classes, IdComponent, SysUtils, IdHTTP;
  TFindWebThread = class(TThread)
    Addr, Text, Status: string;
    procedure Execute; override;
    procedure AddToList;
    procedure ShowStatus;
    procedure GrabHtml;
    procedure HtmlToList;
    procedure HttpWork (Sender: TObject; AWorkMode: TWorkMode;
      const AWorkCount: Integer);
    strUrl: string;
    strRead: string;
{ TFindWebThread }
procedure TFindWebThread.AddToList;
  if Form1.ListBox1.Items.IndexOf (Addr) < 0 then
    Form1.ListBox1.Items.Add (Addr);
    Form1.DetailsList.Add (Text);
procedure TFindWebThread.Execute;
  Status := 'Done with ' + StrUrl;
  Synchronize (ShowStatus);
procedure TFindWebThread.GrabHtml;
  Http1: TIdHTTP;
  Status := 'Sending query: ' + StrUrl;
  Synchronize (ShowStatus);
  Http1 := TIdHTTP.Create (nil);
    Http1.Request.UserAgent := 'User-Agent: NULL';
    Http1.OnWork := HttpWork;
    strRead := Http1.Get (StrUrl);
procedure TFindWebThread.HtmlToList;
  strAddr, strText: string;
  nText: integer;
  nBegin, nEnd: Integer;
  Status := 'Extracting data for: ' + StrUrl;
  Synchronize (ShowStatus);
  strRead := LowerCase (strRead);
    // find the initial part HTTP reference
    nBegin := Pos ('href=http', strRead);
    if nBegin <> 0 then
      // get the remaining part of the string, starting with 'http'
      strRead := Copy (strRead, nBegin + 5, 1000000);
      // find the end of the HTTP reference
      nEnd := Pos ('>', strRead);
      strAddr := Copy (strRead, 1, nEnd - 1);
      // move on
      strRead := Copy (strRead, nEnd + 1, 1000000);
      // add the URL if 'google' is not in it
      if Pos ('google', strAddr) = 0 then
        nText := Pos ('</a>', strRead);
        strText := copy (strRead, 1, nText - 1);
        // remove cached references and duplicates
        if (Pos ('cached', strText) = 0) then
          Addr := strAddr;
          Text := strText;
  until nBegin = 0;
procedure TFindWebThread.HttpWork(Sender: TObject; AWorkMode: TWorkMode;
  const AWorkCount: Integer);
  Status := 'Received ' + IntToStr (AWorkCount) + ' for ' + strUrl;
  Synchronize (ShowStatus);
procedure TFindWebThread.ShowStatus;
  Form1.StatusBar1.SimpleText := Status;
End example

The program looks for subsequent occurrences of the href=http substring, copying the text up to the closing > character. If the found string contains the word google, or its target text includes the word cached, it is omitted from the result. You can see the effect of this code in the output shown in Figure 19.4. You can start multiple searches at the same time, but be aware that the results will be added to the same memo component.

Click To expand
Figure 19.4:  The WebFind application can be used to search for a list of sites on the Google search engine.

The WinInet API

When you need to use the FTP and HTTP protocols, as alternatives to using particular VCL components, you can use a specific API provided by Microsoft in the WinInet DLL. This library is part of the core operating system and implements the FTP and HTTP protocols on top of the Windows sockets API.

With just three calls—InternetOpen, InternetOpenURL, and InternetReadFile—you can retrieve a file corresponding to any URL and store a local copy or analyze it. Other simple methods can be used for FTP; I suggest you look for the source code of the WinInet.pas Delphi unit, which lists all the functions.


The help file of the WinInet library is not part of the SDK Help shipping with Delphi, but can be found online on MSDN at

The InternetOpen function establishes a generic connection and returns a handle you can use in the InternetOpenURL call. This second call returns a handle to the URL that you can pass to the InternetReadFile function in order to read blocks of data. In the following sample code, the data is stored in a local string. When all the data has been read, the program closes the connection to the URL and the Internet session by calling the InternetCloseHandle function twice:

  hHttpSession, hReqUrl: HInternet;
  Buffer: array [0..1023] of Char;
  nRead: Cardinal;
  strRead: string;
  nBegin, nEnd: Integer;
  strRead := '';
  hHttpSession := InternetOpen ('FindWeb', INTERNET_OPEN_TYPE_PRECONFIG,
    nil, nil, 0);
    hReqUrl := InternetOpenURL (hHttpSession, PChar(StrUrl), nil, 0,0,0);
    try // read all the data
        InternetReadFile (hReqUrl, @Buffer, sizeof (Buffer), nRead);
        strRead := strRead + string (Buffer);
      until nRead = 0;
      InternetCloseHandle (hReqUrl);
    InternetCloseHandle (hHttpSession);

Browsing on Your Own

Although I doubt you are interested in writing a new web browser, it might be interesting to see how you can grab an HTML file from the Internet and display it locally, using the HTML viewer available in CLX (the TextBrowser control). Connecting this control to an Indy HTTP client, you can quickly come up with a simplistic text-only browser with limited navigation. The core is

TextBrowser1.Text := IdHttp1.Get (NewUrl);

where NewUrl is complete location of the web resource you want to access. In the BrowseFast example, this URL is entered in a combo box, which keeps track of recent requests. The effect of a similar call is to return the textual portion of a web page (see Figure 19.5), because grabbing the graphic content requires much more complex coding. The TextBrowser control really is better defined as a local file viewer than as a browser.

Click To expand
Figure 19.5:  The output of the BrowseFast text-only browser

I've added to the program only very limited support for hyperlinks. When a user moves the mouse over a link, its link text is copied to a local variable (NewRequest), which is then used in case of a click on the control to compute the new HTTP request to forward. Merging the current address (LastUrl) with the request, though, is far from trivial, even with the help of the IdUrl class provided by Indy. Here is my code, which handles only the simplest cases:

procedure TForm1.TextBrowser1Click(Sender: TObject);
  Uri: TIdUri;
  if NewRequest <> '' then
    Uri := TIdUri.Create (LastUrl);
    if Pos ('http:', NewRequest) > 0 then
      GoToUrl (NewRequest)
    else if NewRequest [1] = '/' then
      GoToUrl ('http://' + Uri.Host + NewRequest)
      GoToUrl ('http://' + Uri.Host + Uri.Path + NewRequest);

Again, this example is trivial and far from usable, but building a browser involves little more than the ability to connect via HTTP and display HTML files.

A Simple HTTP Server

The situation with the development of an HTTP server is quite different. Building a server to deliver static pages based on HTML files is far from simple, although one of the Indy demos provides a good starting point. However, a custom HTTP server might be interesting when building a totally dynamic site, something I'll focus on in more detail in Chapter 20.

To show you how to begin the development of a custom HTTP server, I've built the HttpServ example. This program has a form with a list box used for logging requests and an IdHTTPServer component with these settings:

object IdHTTPServer1: TIdHTTPServer
  Active = True
  DefaultPort = 8080
  OnCommandGet = IdHTTPServer1CommandGet

The server uses port 8080 instead of the standard port 80, so that you can run it alongside another web server. All the custom code is in the OnCommandGet event handler, which returns a fixed page plus some information about the request:

procedure TForm1.IdHTTPServer1CommandGet(AThread: TIdPeerThread;
  RequestInfo: TIdHTTPRequestInfo; ResponseInfo: TIdHTTPResponseInfo);
  HtmlResult: String;
  // log
  Listbox1.Items.Add (RequestInfo.Document);
  // respond
  HtmlResult := '<h1>HttpServ Demo</h1>' +
    '<p>This is the only page you''ll get from this example.</p><hr>' +
    '<p>Request: ' + RequestInfo.Document + '</p>' +
    '<p>Host: ' + RequestInfo.Host + '</p>' +
    '<p>Params: ' + RequestInfo.UnparsedParams + '</p>' +
    '<p>The headers of the request follow: <br>' +
    RequestInfo.RawHeaders.Text + '</p>';
  ResponseInfo.ContentText := HtmlResult;

By passing a path and some parameters in the command line of the browser, you'll see them reinterpreted and displayed. For example, Figure 19.6 shows the effect of this command line:

Click To expand
Figure 19.6:  The page displayed by connecting a browser to the custom HttpServ program

If this example seems too trivial, you'll see a slightly more interesting version in the next section, where I discuss the generation of HTML with Delphi's producer components.


If you plan to build an advanced web server or other Internet servers with Delphi, then as an alternative to the Indy components, you should look at the DXSock components from Brain Patchwork DX (

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